3.20 grading ring of an arrester metal part, usually circular in shape, mounted to modify electrostatically the voltage distribution along the arrester 3.21 high current impulse of an
Arrester identification
Metal-oxide surge arresters for HVDC applications shall be identified by the following minimum information which shall appear on a nameplate permanently attached to the arrester:
– continuous operating voltage where applicable defined by
– rated short-circuit withstand current in kiloamperes (kA) For arresters for which no short- circuit rating is claimed, the sign “0“ shall be indicated;
– residual voltage at specified coordination current (where applicable) given in x kV at y kA;
– the manufacturer’s name or trade mark, type and identification of the complete arrester;
– identification of the assembling position of the unit (for multi-unit arresters only);
– for GIS arresters the rated gas pressure for insulation at 20 °C.
Arrester classification
Surge arresters, covered by this standard, are classified by their location and main protection purpose (e.g valve arrester, d.c bus arrester, neutral bus arrester, etc.)
Normal service conditions
Surge arresters meeting this standard are designed for reliable performance under specific service conditions: they can operate outdoors in temperatures ranging from –40 °C to +40 °C, withstand solar radiation up to 1.1 kW/m², and function indoors in valve halls with temperatures between +5 °C and +60 °C.
The temperature in the valve halls can be maintained below 60 °C, which is relevant for establishing the initial temperature in the thermal recovery test (refer to sections 9.14.3.2 and Annex B) Additionally, the altitude should not exceed 1,000 m, wind speed must be 34 m/s or less, the structure should be vertically erected, and the voltage applied continuously between the arrester terminals should not surpass its continuous operating voltage.
Abnormal service conditions
Surge arresters operating under non-standard conditions necessitate careful design, manufacturing, and application considerations The implementation of this standard in such scenarios requires mutual agreement between the manufacturer and the user Abnormal service conditions may include temperatures exceeding +40 °C for outdoor installations and +60 °C for indoor ones, or dropping below -40 °C; altitudes above 1,000 m; exposure to harmful fumes or vapors that could damage insulating surfaces or mounting hardware; significant contamination from smoke, dirt, salt spray, or other conductive materials; excessive moisture, humidity, or steam; live washing of the arrester; the presence of explosive dust, gas, or fume mixtures; and abnormal mechanical stresses such as earthquakes, vibrations, or high wind velocities.
When considering the installation and operation of arresters, it is crucial to account for various factors such as high ice loads and cantilever stresses, unusual transportation or storage conditions, and the presence of heat sources nearby Additionally, non-vertical or suspended erection methods, torsional and tensile loading on the arrester, and its use as mechanical support must be evaluated Lastly, high magnetic fields resulting from proximity to reactors can also impact the performance of the arrester.
Insulation withstand of the arrester housing
The arrester must be designed to withstand voltages during lightning conduction, switching impulse currents, and anticipated maximum power frequency and d.c overvoltages The external insulation capability of porcelain and polymer-housed arresters should be verified through tests as per section 9.2, while GIS arresters must undergo testing in accordance with section 11.7.4.2 Additionally, the internal insulation withstand capability should be demonstrated through tests outlined in sections 9.15 or 9.14.3.1.
Residual voltage
The measurement of residual voltages aims to determine the maximum residual voltages for a specific design across all defined currents and wave shapes This data is obtained from type test results and the maximum residual voltage associated with a lightning impulse current, as outlined in the routine tests published by the manufacturer.
The maximum residual voltage for a specific arrester design is determined by multiplying the residual voltage from type-tested sections by a designated scale factor This scale factor represents the ratio of the declared maximum residual voltage, verified during routine tests, to the measured residual voltage of the sections under identical current and wave shape conditions.
Manufacturers’ literature shall contain, for each arrester listed, the following residual voltage information:
• Maximum lightning impulse residual voltage at the lightning impulse coordination current of the arrester (see 9.10.3)
• Maximum switching impulse residual voltage at the switching impulse coordination current of the arrester (see 9.10.4)
• Maximum steep current impulse residual voltage, excluding inductive voltage contribution, for an impulse current having peak value equal to the steep impulse coordination current of the arrester (see 9.10.2)
The maximum steep current impulse residual voltage, which includes the contribution from inductive voltage, is determined for an impulse current with a peak value that matches the steep impulse coordination current of the arrester This residual voltage is defined as follows:
Maximum steep current impulse residual voltage (see 9.10.2), excluding inductive voltage contribution + Magnitude of inductive voltage drop (U L ) where U L is calculated as follows:
U L is the peak value of the inductive voltage drop (kV);
L’ is the inductivity per unit length (àH/m);
L’ = 1 for outdoor and indoor arresters except valve arrester;
L’ = 0,6 for valve arresters if located in close vicinity (within a few meters) from the thyristor valves;
L’ = 0,3 for GIS arresters; h is the terminal-to-terminal length of the arrester (m);
T f is the front time of the steep current impulse; equal to 1 às;
I stico is the steep impulse coordination current (kA)
The inductive voltage drop plays a crucial role primarily during steep current impulses, enhancing the protective level of the arrester beyond that of the MO resistor alone This increase in residual voltage, as outlined in section 9.10.2, is particularly relevant for users conducting insulation coordination studies, as it includes the maximum steep current impulse residual voltage with the inductive voltage contribution.
Internal partial discharge
Under normal and dry operating conditions, internal partial discharges shall be below a level that might cause damage to internal parts This shall be demonstrated by tests according to
Seal leak rate
For arresters having an enclosed gas volume and a separate sealing system, seal leak rates shall be specified as defined in 9.8 and item d) of 10.1.
Current distribution in a multi-column arrester and between matched
The manufacturer must define the maximum permissible current difference between the columns of a multi-column arrester, as outlined in item e) of section 10.1, as well as between the currents in arresters within a matched set, according to item f) of section 10.1.
Long term stability under continuous operating voltage
MO resistors shall be subjected to an accelerated ageing test to provide assurance that they will exhibit stable conditions over the anticipated lifetime of the arrester (see 9.11).
Repetitive charge transfer withstand
Arresters shall withstand repetitive charge transfers as checked during type tests (see 9.12)
The repetitive charge transfer withstand is demonstrated on individual MO resistors in the test to verify the repetitive charge transfer rating (see 9.12.2)
In HVDC projects, the extensive use of MO resistors necessitates the verification of charge transfer capability through project-specific tests These tests should not be conducted more than once a year, or alternatively, through sample tests on each manufactured batch of MO resistors utilized in these projects.
NOTE There may be special applications where single event charge transfers cause energy dissipations higher than the rated thermal energy rating.
Thermal energy capability
Arresters, except those with non-significant continuous operating voltage (3.34), shall have a thermal energy rating as checked by type tests (9.14).
Short-circuit performance
Manufacturers must specify a short-circuit current rating for each type of arrester, with a rated value of "zero" only applicable for applications where expected short-circuit currents are below 1 kA, as indicated on the name plate Regardless of the rating, all arresters must undergo a short-circuit test to ensure they do not fail violently and that any open flames self-extinguish within a specified timeframe.
The design of metallic enclosures for GIS-arresters must comply with the standards outlined in 5.103 of IEC 62271-203:2011 or 5.102 of IEC 62271-200:2011 If the arrester features a separate internal enclosure equipped with a pressure-relief device distinct from the metallic vessel, then section 9.3 is applicable In such instances, it is essential to conduct a test solely with the rated short-circuit current.
Requirements on internal grading components
Internal grading components in arresters must endure the stresses encountered during operation, ensuring their impedance remains stable throughout their service life This stability is validated through testing that verifies the thermal energy rating, which includes the internal grading components in the test sections.
Furthermore, the components shall withstand the accelerated ageing and cyclic tests as specified in 9.16
NOTE If the arrester has a non-significant continuous operating voltage, 9.15 applies instead of 9.14.3.
Mechanical loads
General
The manufacturer shall, except for GIS-arresters, specify the maximum permissible terminal loads relevant for installation and service, such as cantilever, torque and tensile loads.
Bending moment
The arrester shall be able to withstand the manufacturer's declared values for bending loads
When determining the mechanical load applied to a surge arrester, the user should consider, for example, wind, ice and electromagnetic forces likely to affect the installation
Surge arresters enclosed within their package should withstand the transportation loads specified by the user in accordance with IEC 60721-3-2, but not less than Class 2M1
NOTE Unlike porcelain-housed arresters, polymer-housed arresters might show mechanical deflections in service.
Resistance against environmental stresses
The arrester shall be able to withstand environmental stresses as defined in 9.6.
Insulating base
When an arrester is fitted with an insulating base, this device shall withstand the requirements of the test of the bending moment (9.5) without damage.
Mean value of breaking load (MBL)
For porcelain-housed arresters the MBL shall be ≥ 1,2 times the specified short-term load
(SSL) (see 9.5.1.4.1) This shall be demonstrated in the bending moment test of 9.5.
Electromagnetic compatibility
Arresters are not sensitive to electromagnetic disturbances and therefore no immunity test is necessary
Surge arresters should not produce significant disturbances under normal dry operating conditions For arresters with a continuous operating voltage exceeding 100 kV peak, compliance must be verified through a radio interference voltage test (RIV) as outlined in section 9.9 Additionally, if the arrester is positioned at a high potential relative to ground, this factor must be taken into account.
End of life
On request from users, each manufacturer shall give enough information so that all the arrester components may be scrapped and/or recycled in accordance with international and national regulations
Measuring equipment and accuracy
The measuring equipment shall meet the requirements of IEC 60060-2 The values obtained shall be accepted as accurate for the purpose of compliance with the relevant test clauses
All power-frequency voltage tests must utilize an alternating voltage with a frequency ranging from 48 Hz to 62 Hz, characterized by an approximately sinusoidal waveform.
Test samples
General
All tests must be conducted on identical arresters, arrester sections, or arrester units, which should be new, clean, and fully assembled, including grading rings if applicable The setup should closely replicate actual service conditions.
For thermal stability verification tests, it is essential that the sections include the maximum number of parallel columns of MO resistors assembled within a single arrester housing according to the specific design.
When tests are made on sections it is necessary that the sections represent the behaviour of all possible arresters within the manufacturer’s tolerances with respect to a specific test
To ensure compliance with testing standards for MO resistors in arresters, samples must cover the highest residual voltage specified For thermal energy rating tests, samples should represent a reference voltage at the lower end of the manufacturer's declared variation range In multi-column arresters, the highest uneven current distribution must be taken into account Additionally, the ratio of the complete arrester's rated voltage to the section's rated voltage, defined as n, dictates that the volume of resistor elements used in tests should not exceed the minimum volume of all resistor elements in the complete arrester divided by n Furthermore, the reference voltage for the test section must equal \( k \times \frac{U_r}{n} \), where \( k \) is the ratio of the minimum reference voltage to the rated voltage of the arrester.
> k×U r /n for an available test sample, the factor n shall be reduced correspondingly (If
When the reference voltage \$U_{ref}\$ is less than \$k \times U_{r}/n\$, the arrester may absorb excessive energy, and such configurations require manufacturer approval For multi-column arresters, current distribution must be measured during impulse current tests, ensuring that the highest current does not exceed the manufacturer's specified upper limit Additionally, for tests on multi-column sections, discharge energy should be adjusted by the factor \$\beta_g/\beta_a\$, where \$\beta_g\$ is the guaranteed current sharing factor and \$\beta_a\$ is the actual current sharing factor In single-column tests, the energy must be increased by the factor \$\beta_g\$ The samples used to verify the repetitive charge transfer rating must be the longest type of metal oxide (MO) resistors, with a 10-kA residual voltage stress of at least \$0.97 \times (U_{10 kA \text{ per mm of MO resistor length}})_{max}\$ If only lower stress samples are available, the transferred charge must be increased by the ratio of the maximum to actual residual voltage stress Finally, the continuous operating voltage, including CCOV, PCOV, and DCOV where applicable, must meet specific requirements to ensure proper thermal recovery during testing.
– The ratio CCOV, PCOV and DCOV (where applicable) to the rated voltage of the section shall be not less than the maximum ratio claimed for the arrester type.
Arrester section requirements
The arrester section for thermal recovery tests shall thermally represent the arrester being modelled Thermal equivalence shall be verified according to the procedure specified in
The continuous operating voltage of the prorated section shall be at least 3 kVpeak
To achieve thermal equivalence, it may be essential to incorporate components that are typically excluded from the design It is crucial to ensure that these additions do not compromise the dielectric strength of the sample during energy or charge injection.
A thermally prorated section may also be a real arrester of the design
In case of designs with two or more MO columns in parallel the thermally prorated section shall contain the same number of parallel columns as the actual arrester
Upon agreement between manufacturer and user the thermally prorated section of a multi- column design arrester may contain only one single column if thermal equivalence is achieved
For GIS arresters (according to 3.19) of multi-column design the thermally prorated section may contain only one single column if thermal equivalence is achieved
An exact drawing of the thermally prorated section shall be published in the test report
The thermally prorated section of the arrester is not restricted to a specific design or material, allowing for variations from the modeled arrester As long as thermal equivalence and adequate dielectric strength for energy and charge injection are maintained, different designs can be utilized without additional requirements.
Testing GIS arresters can be challenging due to their intricate internal design, making it impractical to test samples with multiple MO resistor columns in parallel However, achieving thermal equivalence with single-column sections is more feasible in GIS arresters compared to AIS arresters, thanks to their superior cooling characteristics.
GIS arresters according to 3.19, single-column sections are accepted if thermal equivalence as per Annex A can be proven
The arrester section for internal dielectric strength tests shall represent a sliced portion of the arrester being modelled, including the MO resistors, the housing and the supporting structure
The continuous operating voltage of the prorated section shall be at least 3 kVpeak
The section must precisely replicate the actual arrester in terms of diameters and materials, including the mechanically supporting structure Additionally, the model should incorporate elements like distance holders and spacers that are positioned throughout the arrester Furthermore, the active component must be surrounded by the same medium as that of the real arrester.
A dielectrically prorated section may also be a real arrester or arrester unit of the design
An exact drawing of the dielectrically prorated section shall be published in the test report
For GIS arresters the clause does not apply The internal components of a GIS arrester shall be tested as per 60099-4
8.3.2.3 Section for residual voltage tests
The arrester section for residual voltage tests must consist of a complete arrester unit, a series stack of MO resistors, or a single MO resistor in still air In the case of multi-column arresters, the section can be formed by the actual number of MO resistors or resistor columns in parallel, or it may consist of just one MO resistor or resistor column.
8.3.2.4 Section for the test to verify the repetitive charge transfer rating, Q rs
The arrester section for testing the repetitive charge transfer rating, Q rs, must consist of an individual metal-oxide (MO) resistor, which can be tested either in still air or in the actual surrounding medium of the design, as determined by the manufacturer's discretion.
General
This clause outlines the type tests applicable to both porcelain-housed and polymer-housed surge arresters, unless stated otherwise It includes all tests and procedures relevant to most high-voltage direct current (HVDC) station arresters, with specific exceptions detailed in section 11 Additionally, GIS arresters for direct current bus and line applications are addressed in section 11.7.
Testing with direct current (d.c.) voltage, such as at 1.5 times the nominal d.c voltage, is not specified because these tests cannot be conducted with the MO resistors installed, and the internal design is evaluated separately (refer to sections 9.14.3.1 and 9.15) Additionally, the d.c withstand voltage for external insulation is generally higher compared to switching and power-frequency withstand voltages.
Insulation withstand test on the arrester housing
General
Voltage withstand tests assess the external insulation's ability to endure voltage levels in the arrester housing For alternative designs, the testing parameters must be mutually agreed upon by the manufacturer and the user.
Tests will be conducted under specified conditions and voltages, with the option for manufacturers to substitute the power-frequency voltage test with a switching impulse voltage test It is essential to thoroughly clean the external surfaces of insulating components, and to remove or replace internal parts as detailed in sections 9.2.2 and 9.2.3.
Insulation withstand tests conducted on equipment such as thyristor valves eliminate the need for additional testing on arresters During these tests, the guidelines outlined in sections 9.2.2 and 9.2.3 must be followed for the arrester housing.
If any of the conditions relating dry arc distance to test voltage, as described in 9.2.6, 9.2.7 or
If section 9.2.8 is satisfied, the tests outlined in sections 9.2.6, 9.2.7, or 9.2.8 do not need to be conducted, as the insulation withstand voltage of the arrester will naturally comply with the minimum requirements under these conditions.
Tests on individual unit housings
Tests will be conducted on the longest arrester housing; if this does not reflect the highest specific voltage stress per unit length, further tests will be carried out on the housing with the highest specific voltage stress During testing, the MO resistors must be removed from the housing or substituted with insulators.
Tests on complete arrester housing assemblies
For arresters with a CCOV of 250 kV or higher, testing must be conducted on fully assembled units, substituting MO resistors with resistors or capacitors to achieve similar voltage grading during high current discharges When using MO resistors, they should provide superior protection characteristics compared to the actual resistors It is essential that the selected MO resistors allow for at least 1 A peak during insulation withstand tests While MO resistors can be used for lightning and switching impulse voltage tests, they are not suitable for power-frequency voltage tests Testing should be carried out under realistic conditions, with the arrester positioned on a pedestal at the minimum height.
Ambient air conditions during tests
The voltage to be applied during a withstand test is determined by multiplying the specified withstand voltage by the correction factor taking into account density and humidity (see
Humidity correction shall not be applied for wet tests.
Wet test procedure
The external insulation of outdoor arresters shall be subjected to wet withstand tests under the test procedure given in IEC 60060-1.
Lightning impulse voltage test
The arresters, except capacitor arresters as per 11.12, shall be subjected to a standard lightning impulse voltage dry test according to IEC 60060-1 The test voltage shall be at least equal to:
– The lightning impulse protection level of the arrester (see 3.42) multiplied by:
• For outdoor arresters and arresters installed indoors at a maximum of the daily (24 h) average ambient temperatures during a year T ≤ 40 °C with 1,1 × e1 000/8 150
• For arresters installed indoors at a maximum of the daily (24 h) average ambient temperatures during a year T> 40 °C with 1,1 × e1 000/8 150 × (273 + T)/313 where T is the maximum average ambient temperature in °C
NOTE The factors cover variation in atmospheric conditions and discharge currents higher than coordinating current For altitude above 1 000 m (abnormal service condition) “1 000” in the formulas is replaced by actual altitude
The arrester must undergo fifteen consecutive impulses at the specified test voltage for both polarities It will be deemed successful if there are no internal disruptive discharges and if the external disruptive discharges do not exceed two in each series.
If the dry arcing distance or the sum of the partial dry arcing distances is larger than the test voltage divided by 500 kV/m, this test is not required.
Switching impulse voltage test
Arresters with a CCOV of 250 kV or higher must undergo a standard switching impulse voltage test as specified by IEC 60060-1 Outdoor arresters are to be tested under wet conditions, while indoor arresters should be tested in dry conditions The test voltage must be at least equal to the specified requirements.
– the switching impulse protection level of the arresters (see 3.42) multiplied by:
Outdoor arresters and those installed indoors, where the maximum daily average ambient temperature does not exceed 40 °C, should adhere to the specifications outlined in IEC 60071-2:1996 Specifically, the insulation level must be calculated using the formula \$1.1 \times e^m \times \frac{1000}{8150}\$, where \$m\$ is derived from Figure 9 of the standard Additionally, the value on the abscissa in Figure 9 must be 1.1 times the switching impulse protection level of the arrester.
For indoor arresters subjected to maximum daily average ambient temperatures exceeding 40 °C, the required insulation level can be calculated using the formula \$1.1 \times e^m \times \frac{1000}{8150} \times \left[\frac{273 + T}{313}\right] m\$, where \$m\$ is derived from IEC 60071-2:1996, Figure 9, which illustrates phase-to-earth insulation The value on the abscissa in Figure 9 should be 1.1 times the switching impulse protection level of the arrester.
NOTE 1 The factors cover variation in atmospheric conditions and discharge currents higher than coordinating current For altitude above 1 000 m (abnormal service condition) “1 000” in the formulas is replaced by actual altitude
If the insulation requirements for arresters exceed those established for the protected equipment, the same insulation levels must be applied to the arresters as well.
The arrester must undergo fifteen consecutive impulses at the specified test voltage for both polarities It will be deemed successful if there are no internal disruptive discharges and if the external disruptive discharges do not exceed two in each series.
If the dry arcing distance or the total of the partial dry arcing distances exceeds the value calculated by the equation \$d = 2.2 \times [e^{(U/1069)} - 1]\$, where \$d\$ represents the distance in meters and \$U\$ is the test voltage in kilovolts, then the test is deemed unnecessary.
NOTE 2 The equation is derived from formula G.3 of IEC 60071-2:1996, where U 50 is given as k × 1 080 × ln(0,46 × d+1), k is the gap factor and d is the distance For the purpose of this standard, the gap factor k is assumed to be equal to 1,1, and two standard deviations of 0,05 each are taken into account to achieve the withstand voltage.
Power-frequency voltage test
Arresters with a CCOV of less than 250 kV, along with capacitor arresters, must undergo a power-frequency voltage test Outdoor arrester housings are tested under wet conditions, while indoor arrester housings are tested in dry conditions.
– The test voltage, with a duration of 1 min, shall have a peak value at least equal to:
For outdoor arresters and those installed indoors where the maximum daily average ambient temperature does not exceed 40 °C, the switching impulse protection level should be multiplied by 1.06, or alternatively, the lightning impulse protection level can be applied.
• For arresters installed indoors at a maximum of the daily (24 h) average ambient temperatures during a year T > 40 °C the switching impulse protection level (see 3.42) multiplied with 1,06 × [(273 + T)/313] or the lightning impulse protection level (see
NOTE 1 The factors 1,06 and 0,88 cover variation in atmospheric conditions and discharge currents higher than coordinating current The factor 0.88 is obtained from a coordination factor of 1,15, a test conversion factor of 0,68 from lightning to power-frequency withstand voltage and an altitude factor of 1,13 The factor 1,06 is obtained from a coordination factor of 1,1, a test conversion factor of 0,85 from switching to power-frequency withstand voltage and an altitude factor of 1,13
Capacitor arrester housings must endure a power-frequency voltage for one minute under specific conditions: outdoor arresters should withstand wet conditions, while indoor arresters must handle dry conditions The peak voltage value should equal the switching impulse protection level, as defined in section 3.42, multiplied by the appropriate factor.
• For outdoor arresters and arresters installed indoors at a maximum of the daily (24 h) average ambient temperatures during a year T≤ 40 °C with 1,2
• For arresters installed indoors at a maximum of the daily (24 h) average ambient temperatures during a year T > 40 °C with 1,2 × [(273 +T)/313]
If the dry arcing distance or the total of the partial dry arcing distances exceeds the value calculated by the equation \$d = [1.82 \times e^{(U/859)} - 1]^{0.833}\$, where \$d\$ represents the distance in meters and \$U\$ is the peak value of the power-frequency test voltage in kilovolts, then the test is deemed unnecessary.
NOTE 2 The equation is derived from formula G.1 of IEC 60071-2:1996, where the peak value of U 50 is given as
The formula \$750 \times \sqrt{2} \times \ln(1 + 0.55 \times d^{1.2}\$ calculates the electrical parameters based on distance \$d\$ According to IEC 60071-2 standards, the gap factor \$k\$ is set to 1, the withstand voltage is considered to be 90% of \$U_{50}\$, and a 10% reduction in \$U_{50}\$ is applied for wet conditions compared to dry conditions.
NOTE 3 The factor 1,2 is taken from IEC 60143-1.
Short-circuit tests
All arresters must undergo testing to ensure that failure does not lead to violent shattering of the housing and that any open flames self-extinguish within a specified timeframe Each type of arrester is evaluated with up to four short-circuit current values Additionally, if an arrester features an alternative to a conventional pressure relief device, this arrangement must also be included in the testing process.
The arrester shall be tested in accordance with the procedures and evaluation criteria given in
IEC 60099-4 depending on the type of design the arrester belong to as per the classification in 60099-4
The test currents must be set at 100%, 50%, and 25% of the maximum short-circuit current, with an additional test conducted at 600 A These currents should be applied for their specified durations, except for the 600 Arms test, which is limited to 1 second The ratio of the first current peak to the r.m.s value should comply with IEC 60099-4, allowing the actual ratio for "Design A" arresters as specified in the same standard.
NOTE 1 If the arrester has a rated short-circuit current verified as per IEC 60099-4 no further tests are necessary if
– The actual short-circuit current is less than or equal to the rated short-circuit current and
– The actual duration of the short-circuit current does not exceed 0,2 s
NOTE 2 If the actual maximum short-circuit current is ≤ 6 kArms the test at 50 and 25 % of maximum current need not to be performed.
Internal partial discharge tests
The test will be conducted on the longest electrical unit of the arrester; however, if this unit does not exhibit the highest specific voltage stress per unit length, further testing will be carried out on the unit with the highest specific voltage stress Additionally, the test sample may be shielded to protect against external partial discharges.
NOTE 1 Shielding against external partial discharges should have negligible effects on the voltage distribution
A power-frequency voltage shall be used for the test and be as follows:
– For valve arresters the test voltage (r.m.s value) shall be 0,9/√2 times PCOV
For d.c bus arresters and d.c line/cable arresters, the required test voltage is 1.05/√2 times the PCOV (r.m.s value) This applies to arresters located at the neutral bus on the line/cable side of a smoothing reactor, as well as those without a smoothing reactor, on the electrode line, metallic return, and d.c reactor arresters Alternatively, manufacturers may choose to conduct tests using a d.c voltage of 1.05 times the d.c system voltage.
– For arresters at neutral bus located on the converter side of smoothing reactor (if any) the test voltage shall be (r.m.s value) 1,0/√2 times PCOV
For converter unit and converter unit d.c bus arresters, the test voltage must be set at 0.95 divided by the square root of 2 times the PCOV (r.m.s value) In the case of mid-point d.c bus arresters, mid-point bridge arresters, high voltage (HV) and low voltage (LV) converter unit arresters, as well as arresters positioned between converters, the specified test voltage requirements differ.
– For transformer valve winding arrester the test voltage (r.m.s value) shall be 0,9/√2 times
– For arresters at d.c and a.c filters the test voltage shall be (r.m.s value) 1,05/√2 times the PCOV
– For capacitor arresters (11.12) the test voltage shall be (r.m.s value) 1,05/√2 times the
The power-frequency voltage must be raised to 1.05 times the sample's test voltage and maintained for a duration of 2 to 10 seconds before returning to the test voltage During this period, the partial discharge level should be assessed in accordance with IEC 60270, ensuring that the internal partial discharge measurement does not exceed 10 pC.
If the test is performed as routine test on arrester units or complete arresters the type test need not to be performed
Test of the bending moment
Test on porcelain-housed arresters
The complete test procedure is shown by the flow chart in Annex C
This test evaluates the arrester's capacity to endure the manufacturer's specified bending loads Typically, arresters are not engineered to handle torsional loads; however, if torsional loading occurs, a specialized test may be required, subject to mutual agreement between the manufacturer and the user.
The test shall be performed on complete arrester units without internal overpressure For single-unit arrester designs, the test shall be performed on the longest unit of the design
In cases where an arrester consists of multiple units or has varying specified bending moments at each end, testing must be conducted on the longest unit corresponding to each distinct bending moment, with loads established in accordance with section C.1.
The test shall be performed in two parts that may be done in any order:
– a bending moment test to determine the mean value of breaking load (MBL);
– a static bending moment test with the test load equal to the specified short-term load
To conduct the bending moment test, one end of the sample must be securely attached to a rigid mounting surface of the test equipment, while a load is applied to the free end This load should be directed perpendicularly to the longitudinal axis of the arrester In cases where the arrester exhibits non-axi-symmetrical bending strength, the manufacturer is required to provide details about this asymmetry Consequently, the load should be applied at an angle that maximizes the bending moment on the weakest section of the arrester.
9.5.1.4.1 Test procedure to determine mean value of breaking load (MBL)
Three samples will be tested, with the SSL verification test conducted first, allowing the use of those samples for MBL determination The test samples do not need to include internal parts The bending load on each sample must be gradually increased until breaking occurs within 30 to 90 seconds, where "breaking" refers to the fracture of the housing and any damage to the fixing device or end fittings.
The mean breaking load, MBL, is calculated as the mean value of the breaking loads for the test samples
NOTE The housing of an arrester may splinter under load and may present a handling hazard
9.5.1.4.2 Test procedure to verify the specified short-term load (SSL)
Three samples will be tested, each containing internal components Before testing, each sample must undergo a leakage check and an internal partial discharge test as outlined in section 10.1 If these tests have already been conducted as routine checks, they do not need to be repeated at this stage.
On each sample, the bending load shall be increased smoothly to SSL, tolerance + − 5 0 %, within
The test load should be applied for a duration of 30 to 90 seconds, followed by a maintenance period of 60 to 90 seconds during which deflection measurements are taken After this period, the load must be released smoothly, and the residual deflection should be recorded at specified intervals.
1 min to 10 min after the release of the load
NOTE The housing of an arrester may splinter under load and may present a handling hazard
The arrester shall have passed the test if
– the mean value of breaking load, MBL, is ≥ 1,2 × SSL;
• there is no visible mechanical damage;
• the remaining permanent deflection is ≤ 3 mm or ≤ 10 % of maximum deflection during the test, whichever is greater;
• the test samples pass the leakage test in accordance with item d) of 10.1;
– the internal partial discharge level of the test samples does not exceed the value specified in item c) of 10.1.
Test on polymer-housed arresters
This test applies to polymer housed arresters (with and without enclosed gas volume)
Arresters lacking a specified cantilever strength must undergo terminal torque preconditioning as outlined in section 9.5.2.4.2.2, thermal preconditioning per section 9.5.2.4.2.4, and a water immersion test according to section 9.5.2.4.3 if they are installed outdoors.
The complete test procedure is shown by the flow chart in Annex C
This test evaluates the arrester's capacity to endure the manufacturer's specified bending loads Typically, arresters are not engineered to handle torsional loads; however, if torsional loading occurs, a specialized test may be required, subject to mutual agreement between the manufacturer and the user.
The test must be conducted on complete arrester units with the highest rated voltage For single-unit designs, the longest unit with the highest voltage rating should be tested In cases where an arrester has multiple units or varying specified bending moments at both ends, testing should focus on the longest unit for each distinct bending moment, with loads established as per section C.1 If the longest unit exceeds a certain length, specific considerations will apply.
800 mm, a shorter length unit may be used, provided the following requirements are met:
– the length is at least as long as the greater of
• three times the outside diameter of the housing (excluding the sheds) at the point it enters the end fittings;
– the unit is one of the normal assortment of units used in the design, and is not specially made for the test;
– the unit has the highest rated voltage of that unit of the design
A test in three steps shall be performed one after the other on three samples as follows:
– on all three test samples a cyclic test comprising 1 000 cycles with the test load equal to the specified long-term load (SLL);
Two samples underwent a static bending moment test using a test load equal to the specified short-term load (SSL), which corresponds to 100% of the value of C.3 Additionally, a mechanical preconditioning test was conducted on the third sample in accordance with section 9.5.2.4.2.
– on all three samples a water immersion test as per 9.5.2.4.3
Tolerance on specified loads shall be + − 5 0 %
The test samples shall contain the internal parts
Prior to the test, each test sample shall be subjected to the following tests:
– electrical tests made in the following sequence:
• watt losses measured at ECOV and at an ambient temperature of 20 °C ± 15 K;
• internal partial discharge test according to item c) of 10.1;
• residual voltage test at not less than (0,01 to 1) times the coordinating current; the current wave shape shall be in the range of T 1 /T 2 = (4 to 10)/(10 to 25) às;
– leakage tests in accordance with item d) of 10.1 for arresters with enclosed gas volume and separate sealing system
Routine tests, including the partial discharge test outlined in item c) of 10.1 and the leakage test specified in item d) of 10.1, do not need to be repeated at this time if they have already been conducted.
To conduct the bending moment test, one end of the sample must be securely attached to a rigid mounting surface, while a load is applied to the free end This load should be directed perpendicularly to the longitudinal axis of the arrester In cases where the arrester exhibits non-axi-symmetrical bending strength, the manufacturer must supply details about this asymmetry, and the load should be applied at an angle that maximizes the bending moment on the weakest section of the arrester.
The test shall be performed on three samples The test is performed in three steps
All three samples will undergo 1,000 cycles of bending moments, where each cycle involves loading from zero to a specified long-term load (SLL) in one direction, then to SLL in the opposite direction, and finally returning to zero load The cyclic motion will approximate a sinusoidal form, with a frequency ranging from 0.01 Hz.
The testing machine may require several cycles to achieve the SLL, with the maximum number of cycles determined by the manufacturer It is important to note that these cycles are not counted within the specified 1,000 cycles.
The maximum deflection observed during the test, along with any residual deflection, must be documented Residual deflection should be measured between 1 to 10 minutes following the removal of the load.
Two samples from step 1 will undergo a bending moment test, where the bending load is gradually increased to the specified short-term load (SSL) within a timeframe of 30 to 90 seconds Once the test load is achieved, it will be held for a duration of 60 to 90 seconds while deflection measurements are taken Following this period, the load will be released smoothly.
The maximum deflection during the test and residual deflection shall be recorded The residual deflection shall be measured within 1 min to 10 min after the release of the load
Subject the third sample from Step 1 to mechanical/thermal preconditioning according to
Subject all three samples to the water immersion test according to 9.5.2.4.3
This preconditioning constitutes part of the test procedure of 9.5.2.4 and shall be performed on one of the test samples as defined in 9.5.2.4
The arrester terminal torque specified by the manufacturer shall be applied to the test sample for a duration of 30 s
This portion of the test applies only to arresters for which a cantilever strength is declared
The test does not apply to arresters installed indoors in ambient conditions as per 6.1
The sample is submitted to the specified long-term load (SLL) in four directions and in thermal variations as described in Figures 6 and 7
If, in particular applications, other loads are dominant, the relevant loads shall be applied instead The total test time and temperature cycle shall remain unchanged
The thermal variations consist of two 48 h cycles of heating and cooling as described in
Figure 6 The temperature of the hot and cold periods shall be maintained for at least 16 h
The test shall be conducted in air The temperature shall be measured in the surrounding air inside the test chamber
The static mechanical load applied must match the SLL specified by the manufacturer This load's direction shifts every 24 hours with temperature changes, transitioning from hot to cold or vice versa, as illustrated in Figure 6.
The test may be interrupted for maintenance for a total duration of 4 h and restarted after interruption The cycle then remains valid
Any residual deflection measured from the initial no-load position shall be reported The residual deflection shall be measured within 1 min to 10 min after the release of the load
Tem per at ur e Load Load direction
Figure 7 – Example of the test arrangement for the thermomechanical test and direction of the cantilever load
This portion of the test applies only to arresters for which no cantilever strength is declared
The test does not apply to arresters installed indoors in ambient conditions as per 6.1
The sample is submitted to the thermal variations as described in Figure 6 without any load applied
The thermal variations consist of two 48 h cycles of heating and cooling as described in
Figure 6 The temperature of the hot and cold periods shall be maintained for at least 16 h
The test shall be conducted in air
This test does not apply to arresters installed indoors e.g in valve halls
The test samples shall be kept immersed in a vessel, in boiling deionised water with 1 kg/m 3 of NaCl, for 42 h
NOTE 1 The characteristics of the water described above are those measured at the beginning of the test
NOTE 2 This temperature (boiling water) can be reduced to 80 °C (with a minimum duration of 52 h) by agreement between the user and the manufacturer, if the manufacturer claims that its sealing material is not able to withstand the boiling temperature for a duration of 42 h This value of 52 h can be expanded up to 168 h (i.e one week) after agreement between the manufacturer and the user
After boiling, the arrester must stay in the vessel until the water cools to about 50 °C, maintaining this temperature until verification tests can be conducted It should then be removed from the water and allowed to cool to ambient temperature for no more than three thermal time constants, as indicated in the cooling curves of Annex A The 50 °C holding temperature is only required if there is a need to postpone the verification tests following the water immersion test.
Figure 8 Evaluation tests shall be made within the time specified in 9.5.2.5 After removing the sample from the water it may be washed with tap water
Tests according to 9.5.2.3 shall be repeated on each test sample
The arrester shall have passed the test if the following is demonstrated:
– there is no visible damage;
42 h Time as long as necessary Cooling
In water In open air
The force-deflection curve maintains a positive slope until reaching the SSL value, with minor dips not exceeding 5% of the SSL magnitude Digital measuring equipment must have a sampling rate of at least 10 s⁻¹ and a cut-off frequency of no less than 5 Hz.
Maximum deflection during step 1 and 2 and any remaining permanent deflection after the test shall be reported
After step 3: within 8 h after cooling as defined in Figure 8:
The increase in watt losses, recorded at ECOV and within an ambient temperature variation of no more than 3 K from the initial measurements, should not exceed the higher value of either 20 mW/kV of ECOV or 20%.
– the internal partial discharge measured at a voltage according to 9.4 does not exceed
10 pC; at any time after the above watt losses and partial discharge measurements:
– for arresters with enclosed gas volume and separate sealing system, the samples pass the leakage test in accordance item d) of 10.1;
– the residual voltage measured on the complete sample at the same current value and wave shape as the initial measurement is not more than 5 % different from the initial measurement;
Environmental tests
General
These tests apply to porcelain-housed arresters They do not apply to arresters installed indoors in e.g valve or DC halls under controlled ambient conditions.
Overview
The environmental tests demonstrate by accelerated test procedures that the sealing mechanism and the exposed metal combinations of the arrester are not impaired by environmental conditions
The test shall be performed on complete arrester units of any length
For arresters with an enclosed gas volume and a separate sealing system, the internal parts may be omitted
Arresters that vary solely in length, while sharing the same design, materials, and sealing systems, are classified as the same type of arrester.
Sample preparation
Prior to the tests, the test sample shall be subjected to the leakage check of d) of 10.1.
Test procedure
The tests specified below shall be performed on one sample in the sequence given
The test shall be performed according to test Nb of IEC 60068-2-14
The hot period must maintain a temperature between +40 °C and +70 °C, while the cold period should be at least 85 K lower than the hot period's temperature, with a minimum temperature of –50 °C.
– duration of each temperature level: 3 h;
The test shall be performed according to Clause 4 and Subclause 7.6, as applicable, of
– salt solution concentration: 5 % ± 1 % by weight;
Test evaluation
The arrester shall have passed the tests if the sample passes the leakage check in accordance with item d) of 10.1.
Weather ageing test
General
This test applies to polymer-housed arresters installed outdoors.
Test specimens
The test lasts for 1,000 hours in salt fog conditions and is conducted on the longest electrical unit that has the minimum specific creepage distance and the highest rated voltage as recommended by the manufacturer.
Test procedure
The test involves a continuous, time-limited assessment under salt fog conditions, applying a constant voltage that matches the continuous operating voltage of the arrester For arresters on the d.c side of the converter, a d.c voltage is used, while those on the a.c side are tested with an a.c voltage of 50 or 60 Hz It is essential that the test voltage for d.c voltage arresters is not lower than the DCOV specified for the arrester.
Filter arresters connected to the d.c or a.c side of a converter must undergo testing with an a.c voltage of 50 to 60 Hz This testing should be conducted at an amplitude that is at least equal to the Equipment Category Operating Voltage (ECOV) when subjected to a.c voltages with frequencies exceeding 50 to 60 Hz.
The corrosion test is conducted within a specially designed, moisture-sealed chamber to ensure a controlled environment To facilitate the natural removal of exhaust air, a small aperture of no more than 80 cm² is incorporated into the chamber's design A turbo sprayer or room humidifier with a constant spraying capacity serves as a water atomizer, providing a consistent and reliable means of simulating corrosive conditions.
The fog must fill the chamber without being directly sprayed onto the test specimen A solution of salt water, made from NaCl and deionized water, will be used in the sprayer The test voltage will be generated using a test transformer, and when the test circuit is loaded with a resistive current of 250 mA (r.m.s.) on the high-voltage side, it should not exceed a maximum voltage drop of 5% While specific information on the required d.c source is limited, it is noted that during d.c voltage testing, a current of 250 mA on the high-voltage side should also result in a maximum voltage drop of 5%.
The protection level shall be set at 1 A (r.m.s.) The test specimen shall be cleaned with deionized water before starting the test
The test specimen must be positioned vertically during testing, ensuring sufficient clearance between the chamber's roof and walls to prevent any electrical field disturbances Relevant data can be found in the manufacturer's installation instructions.
– Size of droplets 5 àm to 10 àm
– NaCl content of water between 1 kg/m 3 to 10 kg/m 3
The manufacturer must specify the initial salt content of the water, with the water flow rate measured in litres per hour per cubic metre of the test chamber Recirculation of water is prohibited, although interruptions due to flashovers are allowed If multiple flashovers occur, the test voltage will be interrupted, but the salt fog application must continue until the arrester is washed with tap water Any interruptions in the salt fog application should not exceed 15 minutes, after which the test will restart with a lower salt content If further flashovers happen, this process will be repeated, and interruption times will not count towards the total test duration.
The NaCl concentration in the water, along with the frequency and duration of flashovers, must be recorded Additionally, the count of overcurrent trip-outs should be documented and considered when assessing the overall duration of the test.
Within this salinity range, reduced salt levels may heighten test severity, while elevated salt concentrations raise the likelihood of flashover, complicating testing on larger diameter housings.
Evaluation of the test
The test is considered successful if there is no tracking, erosion does not penetrate through the entire thickness of any shed or external coating, the sheds and housing remain intact, the reference voltage measured before and after the test at the same ambient temperature within ± 3 K does not decrease by more than 5%, and the partial discharge measurement before and after the test is satisfactory, with levels not exceeding 10 pC as per the specified procedure.
For arresters with enclosed gas volume and separate sealing system a successful leakage test in accordance with item d) of 10.1 shall be performed
Seal leak rate test
General
This test applies to arresters having an enclosed gas volume and a separate sealing system
It does not apply to GIS arresters.
Overview
This test demonstrates the gas/water tightness of the complete system
A routine test for seal leak rate, adhering to stringent acceptance criteria, eliminates the need for a type test If the routine test does not meet these criteria, a type test must be conducted on a complete arrester unit, although the internal parts may be excluded from the testing.
If the arrester contains units with differences in their sealing system, the test shall be performed on one unit each, representing each different sealing system.
Sample preparation
The test sample shall be new and clean.
Test procedure
The manufacturer may use any sensitive method suitable for the measurement of the specified seal leak rate
NOTE Some test procedures are specified in IEC 60068-2-17.
Test evaluation
The maximum seal leak rate (see Annex C.4) shall be lower than
Radio interference voltage (RIV) test
Tests are conducted on open-air surge arresters with a Continuous Operating Voltage (CCOV) exceeding 100 kV The evaluation focuses on the longest arrester designed for the specific type, ensuring it operates at the highest continuous voltage.
NOTE 1 A test on an element, part or unit of an arrester cannot be considered adequate because of the nonlinearity of the potential distribution along a complete arrester
NOTE 2 For this test, particular arrester type means also to have identical grading rings configurations
If calculations demonstrate that the electrical field at critical locations for a specific arrester is less than or equal to that of an arrester successfully tested at a higher or equal voltage, then no further testing is necessary.
The test voltage for the different arresters shall be as follows:
The maximum radio interference level for valve arresters, when energized at a power-frequency voltage of 0.9/√2 times the maximum peak value of continuous operating voltage, including high-frequency transients, must not exceed specified limits.
For d.c bus and line/cable arresters, the maximum allowable radio interference level when energized at a power-frequency voltage of 1.05/√2 times the d.c system voltage must not exceed 2,500 µV Alternatively, manufacturers may opt to conduct the test using a d.c voltage of 1.05 times the d.c system voltage, ensuring that both polarities are tested.
For arresters positioned at the neutral bus on the line or cable side of a smoothing reactor, as well as for those at the neutral bus without a smoothing reactor, the maximum allowable radio interference level is determined when the arrester is energized at a power-frequency voltage (r.m.s value).
1,05/√2 times the maximum peak continuous operating voltage including high-frequency transients shall not exceed 2 500 àV
– for arresters at neutral bus located on the converter side of smoothing reactor (if any) the maximum radio interference level of the arrester energized at a power-frequency voltage
(r.m.s value) of 1,0/√2 times the maximum peak continuous operating voltage including high-frequency transients shall not exceed 2 500 àV
For converter unit and converter unit d.c bus arresters, the maximum allowable radio interference level, when energized at a power-frequency voltage of 0.95/√2 times the maximum peak continuous operating voltage, including high-frequency transients, must not exceed 2,500 µV.
For mid-point d.c bus arresters, mid-point bridge arresters, and HV and LV converter unit arresters, the maximum allowable radio interference level when energized at a power-frequency voltage of 0.9/√2 times the maximum peak continuous operating voltage, including high-frequency transients, must not exceed 2,500 µV.
For transformer valve winding arresters, the maximum radio interference level is strictly regulated Specifically, when energized at a power-frequency voltage of 0.9/√2 times the maximum peak continuous operating voltage, including high-frequency transients, the arrester's radio interference level must not exceed 2,500 μV This threshold is crucial in ensuring the arrester's performance and minimizing potential disruptions to radio communications.
For both d.c and a.c filters, the maximum allowable radio interference level for arresters, when energized at a power-frequency voltage of 1.05/√2 times the maximum peak continuous operating voltage, must not exceed 2,500 µV.
– For capacitor arresters (11.12) the maximum radio interference level of the arrester energized at a power-frequency voltage (r.m.s value) of 1,05/√2 times the maximum peak continuous operating voltage shall not exceed 2 500 àV
If the arrester is installed at high potential to ground this should be considered
Surge arresters being tested must be completely assembled and include all standard fittings provided by the manufacturer, such as line and earth terminals and grading rings.
The test voltage shall be applied between the terminals and the earthed base
The earthed components of the surge arrester must be properly connected to the ground It is essential to ensure that nearby earthed or unearthed objects do not interfere with the measurements taken from the surge arresters and the associated testing and measuring circuits.
The test connections and their ends shall not be a source of radio interference voltage of higher values than those indicated below
The measuring circuit shall comply with CISPR 18-2 and CISPR 16-1-1 of the International
Special Committee on Radio Interference (CISPR) The measuring circuit should preferably be tuned to a frequency within 10 % of 0,5 MHz but other frequencies in the range 0,5 MHz to
2 MHz may be used, the measuring frequency being recorded The results shall be expressed in microvolts
When measuring impedances outside the specifications of CISPR publications, they must range between 30 Ω and 600 Ω, with the phase angle not exceeding 20° The equivalent radio interference voltage for 300 Ω can be calculated by assuming a direct proportionality between the measured voltage and the resistance.
The filter F shall have a high impedance so that the impedance between the high-voltage conductor and earth is not appreciably shunted as seen from the surge arrester under test
This filter effectively minimizes circulating radiofrequency currents in the test circuit, which can be generated by the high-voltage transformer or picked up from external sources An optimal impedance value for the filter has been determined to be between 10,000 Ω and 20,000 Ω at the measuring frequency.
To ensure effective testing of surge arresters, it is essential to maintain the radio interference background level at least 6 dB, and ideally 10 dB, below the specified radio interference level of the surge arrester Calibration methods for the measuring instruments used in this process are outlined in CISPR/TR 18-2.
As the radio interference level may be affected by fibres or dust settling on the insulators, it is permitted to wipe the insulators with a clean cloth before taking a measurement
The atmospheric conditions during testing must be documented, as the impact of correction factors on radio interference testing remains unclear However, it is recognized that high relative humidity can significantly affect test sensitivity, and results may be questionable if relative humidity levels exceed acceptable limits.
The following test procedure shall be followed
Residual voltage test
General
The residual voltage type test aims to gather essential data for determining the maximum residual voltages, as detailed in section 7.3 This process involves calculating the ratio of voltages at designated impulse currents to the voltage level assessed during routine tests The voltage measured during these tests represents the residual voltage at an appropriate lightning impulse current.
0,01 to 100 times the lightning impulse coordination current depending on the manufacturer's choice of routine test procedure
The manufacturer's data must specify and publish the maximum residual voltage for lightning impulse current used in routine tests To determine the maximum residual voltages for all specified currents and wave shapes, the measured residual voltages of the test sections are multiplied by the ratio of the declared maximum residual voltage at the routine test current to the measured residual voltage for the same section at that current.
Residual voltage tests must be conducted on the same three samples of complete arresters or arrester sections Adequate time should be allowed between discharges for the samples to cool to near ambient temperature In the case of multi-column arresters, testing can be performed on single-column sections, with residual voltages measured based on total currents divided by the number of columns.
Steep current impulse residual voltage test
A steep current impulse with a peak value equal to the arrester's steep impulse coordination current (±5%) must be applied to each of the three samples The peak value and impulse shape of the voltage across the samples will be recorded and, if needed, adjusted for the inductive effects of the voltage measuring circuit and the geometry of both the test sample and the test circuit.
The following procedure shall be used to determine if an inductive correction is required:
A steep current impulse will be applied to a non-ferrous metal block that matches the dimensions of the tested resistor samples The peak value and shape of the voltage across the metal block will be documented.
If the peak voltage on the metal block is below 2% of the peak voltage of the MO resistor samples, there is no need for inductive correction in the MO resistor measurements.
– If the peak voltage on the metal block is between 2 % and 20 % of the peak voltage on the
To obtain the corrected MO resistor voltages, subtract the impulse shape of the metal block voltage from the impulse shape of each MO resistor voltage, and then record the peak values of the resulting impulse shapes.
If the peak voltage on the metal block exceeds 20% of the peak voltage on the MO resistor samples, improvements must be made to the test circuit and the voltage measuring circuit before repeating the test.
NOTE 1 A possible way to achieve identical current wave shapes during all measurements is to perform them with both the test sample and the metal block in series in the test circuit Only their positions relative to each other need to be interchanged for measuring the voltage drop on the metal block or on the test sample
The maximum steep current impulse residual voltage of the arrester is defined as the highest of the three measured residual voltages, adjusted as needed, and multiplied by the scale factor This measurement excludes any contributions from inductive voltage.
The maximum steep current impulse residual voltage, including inductive voltage contribution, of the arrester is calculated as per 7.3
NOTE 2 Connecting leads to connect the arrester to the power system will introduce additional inductive voltage drop for steep current impulse currents.
Lightning impulse residual voltage test
Each of the three samples will undergo a lightning current impulse test at three peak values: approximately 0.5, 1, and 2 times the lightning impulse coordination current of the arrester The virtual front time must be maintained between 7 µs and 9 µs, while the half-value time can have any tolerance Residual voltages will be measured according to section 7.3, and the maximum residual voltages will be plotted on a curve against discharge current The residual voltage corresponding to the lightning impulse coordination current on this curve is defined as the lightning impulse protection level of the arrester.
If a full arrester routine test cannot be performed at the specified currents, additional type tests must be conducted at a current between 0.01 and 0.25 times the lightning impulse coordination current for comparison with the complete arrester.
Switching impulse residual voltage test
Each of the three samples must undergo a switching current impulse with a peak value equal to the switching impulse coordination current, within a tolerance of ±5% The virtual front time should range from 30 µs to 100 µs, while the half-value time can have any tolerance The residual voltages are measured according to specified standards.
7.3 The highest of these three voltages is defined as the switching impulse protection level of the arrester.